Can you please copy-past the value of /etc/network/interfaces ?
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DJYodDec 21 '12 at 9:12

Can you ping 8.8.8.8 ? If that is the case your DNS isn't working but lowlevel TCP/IP is OK. (The telnet error may be confusing the matter here. Could be NOT indicative of the real problem.) If the ping 8.8.8.8 (Google DNS server) also gives a no route the router also most likely the culprit, but I would suspect the NAT/routing part in stead of the DNS service.
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TonnyDec 21 '12 at 9:19

You'll most probably want to change your dns-nameserver - if you don't know what that is, just use 8.8.8.8. I would assume your IP settings are ok so no need to change them. Also update the dns-search and dns-domain and append your internal domain name. If you update your resolv.conf file, it may get over ridden when your network services restart as the resolvconf package will take what is placed in your interfaces file and put them in to your resolv.conf file. Thus the problem may reappear. Also the routers firewall may be blocking ports or not serving DNS. Which is why you could try 8.8.8.8. This will give you external DNS resolution. If internal DNS isn't working, then you need to ensure a DNS server is contactable and running. Otherwise use the /etc/hosts file.